1. Technical Field
The present invention relates in general to a circuit and method for measuring frequency response on an integrated circuit. In particular, the present invention relates to a system and method for measuring frequency response at specific integrated circuit locations.
2. Description of the Related Art
Many modern data processing systems include multiple central processing unit cores (CPUs) located on a single semiconductor substrate of an integrated circuit. Data processing systems including such integrated circuits will execute instructions of a single program across these multiple CPUs. One technique to employ the multiple CPUs in the execution of these instructions is to divide the instructions into groups of instructions or threads. Then each group or thread is directed to a central processing unit for execution. In directing a thread to a specific CPU for its instruction execution, it is desirable to determine which CPU would be able to execute the instructions most efficiently. The co-pending patent application “Using IR Drop Data for Instruction Thread Direction,” (pending patent application Ser. No. 11/671,613) addresses this feature. This co-pending application is related to several other co-pending patent applications which address the measurement of physical characteristics on an integrated circuit in order to regulate supply voltage, predict performance and address other functions. These other co-pending patent applications include On-Chip Adaptive Voltage Compensation,” (pending patent application Ser. No. 11/671,485); “Using Performance Data for Instruction Thread Direction,” (pending patent application Ser. No. 11/671,627); “Using Temperature Data for Instruction Thread Direction,” (pending patent application Ser. No. 11/671,640); “Integrated Circuit Failure Prediction,” patent application Ser. No. 11/671,599 issued as U.S. Pat. No. 7,560,945); “Instruction Dependent Dynamic Voltage Compensation,” (pending patent application Ser. No. 11/671,579); “Temperature Dependent Voltage Source Compensation,” (pending patent application Ser. No. 11/671,568); “Fan Speed Control from Adaptive Voltage Supply,” (pending patent application Ser. No. 11/671,555); and “Digital Adaptive Voltage Supply,” (pending patent application Ser. No. 11/671,531 issued as U.S. Pat. No. 7,714,635); each assigned to the IBM Corporation and herein incorporated by reference.
In a co-pending patent application entitled “Half Width Counting Leading Zero Circuit” also assigned to IBM and herein incorporated by reference, a more efficient count leading zero circuit is disclosed which can be used as part of a frequency response measurement circuit disclosed in this application. In addition, a second co-pending patent application entitled “Data Correction Circuit” (pending patent application Ser. No. 11/844,405) also assigned to IBM and herein incorporated by reference, addresses a correction circuit that is used to correct input values to the count leading zeros circuit.
One physical condition of the CPUs for determining performance is the variation in the frequency response of a semiconductor substrate portion containing the CPU. Such variation in the frequency response is inherently due to the manufacturing process. The number of CPU cores that can be implemented on a single semiconductor substrate is proportional to the area of the single semiconductor substrate. In a single semiconductor substrate with large area, the performance of individual devices contained in cores that are not within close spatial proximity differs due to minor changes in semiconductor manufacturing process across the single semiconductor substrate. The net effect of this is that CPUs that are separated offer different frequency responses or performance. Usually, the higher measured frequency response will indicate a more efficient central processing unit.
One way to address this difference in performance of the CPUs across the single semiconductor substrate is to measure frequency response at these different CPU locations. This was accomplished in the above co-pending patent applications by using a loop oscillator which generates an output frequency. This frequency is analyzed along with other physical characteristics of the CPU to predict instruction execution performance. This performance information can be used to direct instruction threads to specific CPUs for a faster instruction execution. FIG. 1 is a block diagram of an adaptive voltage supply that could be configured to provide this performance information.
The loop oscillator output frequency must be analyzed to determine its performance component. When using digital circuitry, this loop oscillator frequency output, an analog output, must be converted to a digital form before the performance can be determined. What is needed is a more direct way to indicate this frequency response performance component.